Platinum clad tantalum anode assembly

ABSTRACT

A platinum-clad tantalum anode assembly includes a tantalum mesh having platinum-cladding on the surface thereof to be disposed adjacent the workpiece, a conductive framework disposed adjacent the other surface of the tantalum mesh, and an electrical distribution subassembly. The framework includes a plurality of elongated tantalum frame members conductively bonded to the mesh and transverse tantalum frame members extending perpendicularly thereto. The electrical distribution subassembly includes at least one elongated bus member extending generally parallel to the elongated frame members and at least one transverse bus member extending generally perpendicular thereto. At least one of the transverse bus members is disposed intermediate the ends of the elongated frame members and conductively bonded on one surface thereof to the elongated bus member and on the other surface thereof to the elongated frame members. The bus members are free from electrical contact with the framework and mesh except for the conductive path provided by the bonds between the transverse bus member and the elongated frame members, and the bonds are resistant to corrosive action by a bath in which the assembly may be disposed. The assembly is useful in the high speed continuous electroplating of carbon steel and other substrates with various metals such as tin and chromium.

United States Patent Rogers et al.

[ Dec. 24, 1974 PLATINUM CLAD TANTALUM ANODE ASSEMBLY [75] Inventors:Orris A. Rogers, Woodbury;

Eldridge K. Camp; John P. Borgmann, both of Litchfield, all of Conn.

[73] Assignee: American Chemical & Refining Company, Incorporated,Waterbury, Conn.

[22] Filed: Nov. 21, 1972 [21] Appl. No.: 308,478

[52] US. Cl 204/286, 204/28, 204/206 [51] Int. Cl. C23b 5/72, C23b 5/58[58] Field of Search 204/286 [56] References Cited UNITED STATES PATENTS3,49l,014 l/l970 Bianchi et al 204/242 3,672,973 6/l972 DeNora et al.204/279 X 3,677,917 7/1972 Martinson 204/99 3,677,929 7/1972 Young204/286 3,689,384 9/1972 Barbato et al. 204/99 OTHER PUBLICATIONSElectroplating Engineering Handbook, 2nd Ed., by Graham et al., pp. 554,555, pub. by Reinhold, New York, 1962, copy AUl 14.

Primary Examiner-F. C. Edmundson [57] ABSTRACT A platinum-clad tantalumanode assembly includes a tantalum mesh having platinum-cladding on thesurface thereof to be disposed adjacent the workpiece, a

conductive framework disposed adjacent the other surface of the tantalummesh, and an electrical distribution subassembly. The framework includesa plurality of elongated tantalum frame members conductively bonded tothe mesh and transverse tantalum frame members extending perpendicularlythereto. The electrical distribution subassembly includes at least oneelongated bus member extending generally parallel to the elongated framemembers and at least one transverse bus member extending generallyperpendicular thereto. At least one of the transverse bus members isdisposed intermediate the ends of the elongated frame members andconductively bonded on one surface thereof to the elongated bus memberand on the other surface thereof to the elongated frame members. The busmembers are free from electrical contact with the framework and meshexcept for the conductive path provided by the bonds between thetransverse bus member and the elongated frame members, and the bonds areresistant to corrosive action by a bath in which the assembly may bedisposed.

The assembly is useful in the high speed continuous electroplating ofcarbon steel and other substrates with various metals such as tin andchromium.

9 Claims, 8 Drawing Figures BACKGROUND OF THE INVENTION Large metallicanodes for use in the tin and chromium plating of carbon steel strips onhigh speed continuous lines have been fabricated from a variety ofdifferent materials including solid tin, lead, stainless steel andplatinized titanium. Corrosion of the currentcarrying anode results inthe need for periodic replacement of the solid tin anode at all toofrequent intervals. Stainless steel anodes have displayed poorelectrical properties and in various baths are somewhat susceptible bothto corrosive attack and the formation of inert coatings on the anodewhich further reduce utility. The platinized titanium anode exhibits ashort useful life as discontinuities and pinholes in the platinumcoating permit destruction of the anode through corrosive attack on thetitanium base. The magnitude of the prob lem becomes readily apparentwhen one learns that the platinized titanium anode life in fullproduction operation in high speed baths may be less than 25 days andthe replacement cost thereof may be many thousands of dollars.

Among the most important criteria to be considered in selection of anappropriate anode is the ability of the anode to operate so as toprovide relatively high current densities for high electroplating speedand to provide fairly uniform current distribution over its activesurface to ensure uniformity of electrodeposits on the workpiece. Toobtain high current densities a series of electroplating tanks eachcontaining short anodes often has been used rather than a singleelongated anode providing the desired plating distance. To achieveuniformity of electrodeposits, the anode to cathode dis tance has beenvaried over the length of the plating path to compensate for thegradient in current distribution over the surface of the anode; this isan expediency which compensates for, but does not solve, the problem ofmaintaining a uniform current distribution over the working anodesurface.

An additional problem encountered in providing the large elongatedanodes desired for use on high speed continuous electroplating lines hasbeen the lack of rigidity in noble metal anode screens or mesh and otherlightweight structures. Attempts to minimize waving by providingphysical support by frames have tended to impede a desirably highelectroplating solution flow. while the use of mesh anodes to reduceresistance to solution flow has merely increased the problem of wavingdue to the flexibility of the mesh.

Accordingly, it is an object of the present invention to provide a novelanode assembly resistant to corrosive attack on the operating surfaceand providing substantially uniform current distribution over thesurface thereof.

It is also an object to provide an anode assembly which provides highlydesirable electrical properties and which will avoid spurious electricalconduction into the bath.

Another object is to provide a platinum-clad anode assembly which may befabricated from components readily and which exhibits relative rigidityduring operations.

Still another object is to provide such an anode assembly having a lifein full production operation of at least three months, which can operateat current densities as high as 30 kiloamperes per square meter andwhich will not be destroyed by the attach of electroplating solution.

A further object is to provide in such an anodic as sembly a large andelongated anode working surface having a variation in currentdistribution from point to point over its surface of less than 20 percent.

SUMMARY OF THE INVENTION It has been found that the foregoing andrelated objects may be readily attained in a platinum-clad tantalumanode assembly which has a tantalum mesh having platinum cladding on onesurface thereof, and a conductive framework disposed adjacent the othersurface. The framework includes a plurality of elongated frame membersand transverse frame members extending perpendicularly thereto, theframe members being fabricated of tantalum and the mesh being bonded tothe elongated frame members to provide electrical connectiontherebetween resistant to corrosive action by a bath in which theassembly may be disposed.

The assembly further provides a current distribution subassembly havingat least one elongated bus member extending generally parallel to theelongated frame members and at least one transverse bus member extendinggenerally perpendicular thereto and disposed intermediate the ends ofthe elongated frame members. The transverse bus member is bonded on onesurface thereof to the elongated bus member and on the other surfacethereof to the elongated frame members to provide electrical connectiontherebetween resistant to corrosive action by a bath in which theassembly may be disposed. The bus members are free from electricalcontact with the framework except through the conductive paths providedby the bondls between the transverse bus members and the elongated framemembers.

Preferably a plurality of elongated and transverse bus members areprovided, all fabricated of tantalum, with at least a plurality of thetransverse bus members being disposed intermediate the ends of theelongated frame members so that current may be selectively applied at aplurality of points intermediate the length of the framework. Thetransverse frame members are preferably disposed adjacent the ends ofthe elongated frame members and bonded thereto to provide rigidity. In apreferred embodiment the mesh is comprised of a plurality of strips withat least two of the mesh strips being bonded to one elongated framemember.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view ofplatinum-clad tantalum anode assembly embodying the present invention,with a reinforcing frame shown in phantom line;

FIG. 2 is a side elevational view of the anode assembly shown in FIG. 1;

FIG. 3 is a front elevational view to a reduced scale of the electricalcurrent distribution subassembly with the insulator strips shown inphantom line;

FIG. 4 is a side elevational view of the subassembly of FIG. 3;

FIG. 5 is a front elevational view of the insulator strips used in thesubassembly of FIG. 3;

FIG. 6 is a fragmentary front elevational view to a reduced scale of themesh and mesh-supporting framework of FIG. 1;

FIG. 7 is a side elevational view of the mesh and framework of FIG. 6;and

FIG. 8 is a schematic view illustrating the use of the anode assembliesof the present invention in an electroplating installation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As previously indicated, theplatinum-clad tantalum anode assembly of the present invention iscomprised of a platinum-clad tantalum mesh, a conductive framework andan electrical current distribution subassembly. The entire anodeassembly is shown in FIGS. 1 and 2, with the subassembly of mesh andframework being shown in greater detail in FIGS. 6 and 7 and the currentdistribution subassembly being shown in detail in FIGS. 3 and 4. Forease of discussion, the mesh and framework subassembly shown in FIGS. 6and 7 will first be described.

Referring now to FIGS. 6 and 7, elongated mesh strips 10 are fabricatedfrom a tantalum mesh bearing on one surface a thin platinum cladding.Five of these elongated platinum-clad tantalum mesh strips 10 aresupported by the conductive structural framework generally designated bythe numeral 12 and which includes six elongated tantalum frame members14a-14f and two transverse tantalum frame members 16, 18. Theplatinum-clad tantalum mesh strips 10 extend between and slightlyoverlap pairs of elongated frame members 14 (for example, one strip 10between elongated frame members 14a and 14b), and the overlapping areasare welded together. As will be appreciated, the'platinumclad surface ofthe strips 10 is exposed so that the weld is of tantalum to tantalum toavoid formation of undesirable intermetallic compounds. Strip edgewelding is preferably used to preserve full electrical conductivitybetween the strips 10 and the elongated frame members 14.

Top and bottom transverse frame members 16, 18 are subsequently weldedin place over the end portions of mesh strips 10 and frame members 14 toprovide an electrically conductive, structurally sound framework for themesh 10. A thin tantalum strip 20 is also welded to the rear bottomsurface of frame members 14, parallel to the transverse frame member 18,to provide additional rigidity to the frame 12. If desired, thin narrowtantalum strips may be welded over the exposed front surfaces of theelongated frame members 14b through 14c and partially overlapping thewelded edges of the mesh strips 10 to protect the edges of the exposedmesh strips, to stiffen the frame even further and to provide a morefinished appearance.

Turning now to FIGS. 3 and 4, the electrical current distributionsubassembly generally designated by the numeral 30 has three elongatedbus members 32, 34 and 36 extending generally parallel to the elongatedframe members 14 (as illustrated in FIG. 1), and three transverse busmembers 38, 40 and 42 extending generally perpendicular to the elongatedbus members. The transverse bus members 38, 40, 42 are conductivelybonded or welded onto the surface of the elongated bus members 32, 34,36 adjacent the framework 12. Welds have been made at each point ofintersection although, in other embodiments where a different currentdistribution may be desired, one or more points of intersection betweenthe elongated and transverse bus members may be insulated to avoidconductive action. The welded busbars provide a rigid electrical networkadapted to carry current substantially uniformly to points spacedtherealong. Each of the elongated busbars 32, 34, 36 is provided with apair of apertures 44 adjacent the upper end thereof for a purpose to bedescribed hereinafter.

As illustrated, the transverse bus member 38 is disposed above theframework 12 and will in operation be above the level of theelectroplating solution; its purpose is to ensure uniformity of currentdistribution through the several elongated bus members 32, 34, 36 and toavoid arcing therebetween. The transverse bus members 40, 42 are bondedto the framework 12 as will be discussed more in detail hereinafter.

As seen in FIGS. 35, the faces of the elongated bus members 32, 34, 36adjacent the framework 12 have mounted thereon synthetic plasticinsulator strips 50, 50' which extend between framework 12 andelectrical current distribution subassembly except in the areas of thetransverse bus members 40, 42. As can be seen, the elongated bus members32, 34, 36 are provided with a multiplicity of apertures 37 whichcooperate with similar apertures 51 in the insulating strips 50, 50' sothat engagement therebetween may be effected by fasteners 58 seatedtherein as seen in FIG. 2. These insulator strips 50, 50' precludearcing between the bus members 32, 34, 36 and the framework 12 and mesh10 and current flow therebetween through the solution during the initialperiod of operation of the anode assembly in the electroplatingsolution. After the anode assembly has been operative in the bath, theexposed surfaces of the tantalum will develop a non-conductive compoundthereon which will effectively preclude such spurious currentconduction.

Referring now to FIGS. 1 and 2, it can be seen that the framework 12 iswelded to the surface of the electrical current distribution subassemblyby locating the transverse bus members 40, 42 intermediate the ends ofthe elongated frame members 14 and welding them to the back of theelongated frame members 14b through l4e which they contact. The meshstrips 10 may also be welded to the transverse bus members 40, 42 alongtheir opposed surfaces. It will be noted that due to the presence of theinsulator strips 50, 50 at initial use of the assembly and to thedeactivation of the tantalum surfaces after use of the assembly, theonly effective electrical connection between the electrical distributionsubassembly 30 and the conductive structural framework 12 is through thetransverse bus members and 42 which are located intermedite the ends ofthe framework 12. a

The anode formed by the mesh 10, conductive framework 12 and theelectrical current distribution subassembly 30 is mounted upon the maincopper bus conductor 46 shown in FIG. 1 by copper bolts 48 passingsuccessively through a protective copper plate 52, the apertures 44 inthe upper ends of the elongated bus members 32, 34, 36 and the maincopper bus conductor 46. A single copper conductor bar 54 is disposed inconductive contact with the main bus conductor 46 to supply current tothe entire anode assembly.

Referring now to FIG. 1, a reinforcing frame generally designated by thenumeral 56 (shown in phantom) is preferably constructed about theframework 12 of the anode assembly to facilitate handling and mountingof the assembly to protect the elements of the assembly, and to impartgreater rigidity to the assembly. The reinforcing frame 56 is preferablycomposed of four fiberglass-reinforced synthetic plastic strips 56a,56b,

56c, 56d which have channels to receive the elongated frame members 140,14f and the transverse frame members 16, 18; the strips 56a-56d beingheld together by fasteners 57. The reinforcing frame 56 is thus securelyand removably attached directly to the assembly framework withoutappreciably impeding solution flow therethrough.

It will be noted that none of the materials used in the construction ofthe assembly is destructively attacked within the operating limits ofthe plating bath, but the exposed tantalum surfaces will form adesirable, inert nonconductive compound (possibly tantalum oxide) at theinterface with the electroplating bath and this non-conductive compoundprevents spurious conduction and consequent loss of control over anodeoperation. The tantalum has a sufficiently high electrical breakdownpotential to accept a process voltage of 25 volts and even higher whilemaintaining its resistance to chemical attack, and the thermalconductivity of tantalum is high enought to ensure adequate cooling ofthe assembly by convection and conduction of heat to the electroplatingsolution. Additional advantages of the use of annealled metallurgicalgrade tantalum are its relative flexibility and its ability to bestrip-edge welded to preserve full electrical conductivity.

Moreover, by having the platinumclad mesh, the platinum surface willprovide the desired continued high electrical conductivity andresistance to corrosive attack for extended periods of operation. Evenif the cladding develops a pinhole, the thus exposed tantalum willrapidly develop a protective coating.

The overall weight of the assembly (including the anode and the main busconductor) is extremely light in relation to the overall working anodesurface provided. For example, an assembly with an anode surface of 0.8by LS meters weighs only about 11 kilograms.

The platinum-clad tantalum anode assembly 80 described in detail isparticularly useful in the high-speed continuous electroplating ofcarbon steel strip with tin and chromium. Referring now to FIG. 8, anelectroplating tank generally designated by the numeral 82 is equippedwith an inlet 84 and an outlet 86 for rapid circulation of anelectroplating solution 87 therethrough. A discharge weir 85 controlsthe level of the solution in the tank 82.

A carbon steel workpiece 88 is guided by means of rolls 90 down into thesolution within electroplating tank 82, around roll 92 and back out ofthe solution through rolls 94. Anode assemblies 80 are disposed inparallel pairs on opposite sides of the travel path ofthe workpiece 88,with equal lengths of the assemblies being located below the bath level.The upper portion of each assembly 80 (starting with transverse busmember 38 and including all the copper components) is maintained abovethe level of solution 87 within tank 82, and an electrical potential ofabout 5 to 25 volts is applied across the workpiece 88 by means ofelectrical connection to the rolls 90, 94 and to the anode assemblies80.

As the workpiece 88 passes through the tank 82, current flows throughthe bath from the anode assemblies 80 to the workpiece 88 through theelectroplating solution and causes deposition of the metal onto thesurface thereof. The current flow to the anode assembly of the presentinvention intermediate its operative length ensures substantiallyuniform current flow over the effective plating area and a desirablycontrolled deposit. The

pattern and degree of distribution across the effective plating area isdependent on the number and placement of the transverse bus bars 40, 42intermediate the ends of the elongated frame members 32, 34, 36.Accordingly, where a uniform current pattern exhibiting a high degree ofcurrent distribution is desired, a single transverse bus member may belocated about midway along the length of the elongated frame members 32,34, 36, or a plurality of transverse bus members may be somewhatregularly spaced out along such length.

The low weight of the anode assembly facilitates handling of theassembly for inspection, repair and replacement, while the highmechanical strength of the assembly prevents waving" of the anode meshin the bath without undesirably high resistance to solution flowtherethrough.

It will be noted that the anode assembly consists essentially ofplatinum (a highly conductive but chemically resistant anode surfacematerial), tantalum (a strong and highly conductive material which ishighly chemically resistant to destructive corrosion, polypropylene (ahigh-density, heatresistant plastic useful both as a structural framemember and as electrical insulation), threaded plastic fasteners (suchas polypropylene tetrofluoroethylene), fiberglassreinforced plastic (aninert structural backing), and, only above the level of theelectroplating solution, copper bus members.

To effect particular current distribution patterns over the anode meshsurface of the assembly, one or more of the areas of intersectionbetween the elongated bus members 32, 34, 36 and the transverse busmembers 40, 42 may be non-welded and insulated to prevent current flowtherebetween. In this manner, high potential may be applied across theanode surface either to provide a point-to-point current differential ofless than 20 per cent over a large anode surface, or alternatively, in adesired predetermined pattern. to increase plating efficiency, platingspeed or deposit uniformity or to produce a controlled non-uniformity.For example, a non-uniform current distribution pattern may be desiredto compensate for a variable anode/cathode separation.

The anode assemblies of the present invention have utility in theplating of various metals with electrolytes which would attack thetantalum surface to provide the desired non-conductive inert coating andwhich processes employ potentials within a range of about 5 to 25 volts.Because of the special demands of high speed tin and chromium platinginstallations, the anode assemblies of the present invention areparticularly advantageously employed therefor.

Use of the anode assemblies in halide ion containing baths should beavoided since these ions will attack the anode assembly. The preferredelectrolytes are phenylsulfonic acid and its derivatives,naphthylsulfonic acid and its derivatives, sulfate salts, chromatesalts, and other conventional electrolytes which are adapted to providethe desired inert surface compound on the tantalum. ln tin and chromiumplating, di-hydroxy-diphenyl sulfonic acid and ethoxylated naphtholsulfonic acid and their derivatives have been found particularlyadvantageous.

A typical electroplating installation will also include a mixing tankfor the electroplating solution for additions of the metal being platedand other makeup ingredients to be added. The electroplating solution iscirculated through the mixing tank and filtration apparatus in asubstantially continuous fashion. Ideally, the volume of electroplatingsolution flowing through the tank is maintained substantially constantwhile variations in thickness of metal deposits are effected by changingthe rate of travel of the workpiece through the bath while maintainingconstant current density or by changing the applied current with thespeed of the workpiece through the bath being held constant.

As an illustration of the advantages of the anode assembly of thepresent invention, an anode assembly having a working surface of 0.8 by1.5 meters will exhibit a current flow of 4,000 amperes upon applicationof volt potential. In a plating test, a carbon steel strip 0.1 meter inwidth transported through an electroplating installation similar to thatillustrated in FIG. 8 is found to have a plated deposit of 0.75 to 3.00micrometers when the travel is varied from 90 to 380 meters per minute.Current efficiencies using such an anode in a tin plating bath areobserved at 90 to 97 per cent and the current density is variable from0.2 to 2.0 kiloamperes per square meter by variation of the appliedpotential.

Illustrative of the use and advantages of the anode assemblies of thepresent invention are the following examples.

EXAMPLE ONE Tin is electroplated onto a 100 cm. wide carbon steel stripin a l.5 meter deep tank using platinum-clad tantalum anode assembliesshown in FIGS. 1 and 2. Each assembly has a tantalum mesh base of 1.61millimeters thickness and a platinum cladding of 6.35 micrometersthickness; the working anode surface is about 0.85 by L40 meters. Allmetal parts of the conductive structural framework and the electricalcurrent distribution subassembly are fabricated of tantalum. Theassemblies are constructed to have a maximum variation in electricalemissivity from point-to-point across the anode working surface of 20per cent.

The anode/cathode distance in the tank is 0.05 meters. Tin is put intosolution in a heated mixing tank and the solution is purified andcirculated back to the electroplating tank. The plating solution usesethoxylated naphthol sulfonic acid as the electrolyte. The circulationrate of the electroplating solution is maintained constant at about1,135 liters per minute with the workpiece travel speed being variedfrom 90 to 1,000 meters per minute to vary the thickness of the electrodeposits from 0.75 to 3.0 micrometers. The solution is maintained at a4550 C temperature by chilling as necessary.

Application ofa 20 volt potential across the assembly and the workpieceprovides a current density of about 4 kiloamperes per square decimeter.The cathode current efficiency of the bath is found to be about 90-97per cent.

Inspection of the anode assembly after a week of usage shows nocorrosive action except for the desired inert surface compound on theexposed tantalum.

EXAMPLE TWO Chromium is electroplated onto carbon steel in the mannerindicated in Example One except that a dihydroxy-di-phenyl sulfonic acidis used as the electrolyte. The platinum-clad tantalum anode assemblyoperates uniformly and evidences no significant attack after extendedusage except the formation of the inert compound upon the surface of thetantalum.

Thus, it can be seen from the foregoing detailed specification andexamples that the present invention provides a large metallic anodeassembly which provides superior electrical properties and resists bothunwanted corrosion and unwanted formation of inert coatings on itsactive surfaces. The platinum-clad anode of the present invention has amuch longer life in full production operation than a comparableplatinum-clad titanium anode (over three times as long), operates athigh current densitites (about 20 to 50 amperes per square decimeter),and has a tantalum substrate which forms its own protective coating toresist the attack of elec troplating solution through discontinuitiesand pinholes in the platinum cladding. Most importantly, in the novelelongated anode assembly, high current is applied to selected pointsalong the length and width of the anodic working surface to maintain avariation in current distribution of less than 20 per cent frompointto-point across the surface, thereby permitting the maintenance ofhigh current density, the use of faster electroplating speeds and theobtaining of more uniform electrodeposits on the workpiece. Thelightweight but structurally sound anode assembly of the presentinvention is particularly useful in the high speed continuouselectroplating of carbon steel with tin and chromium.

Having thus described the invention, we claim:

I. A platinum-clad tantalum anode assembly comprising:

a relatively flexible tantalum mesh having platinum cladding on only onesurface thereof and a tantalum surface;

a relatively rigid framework disposed adjacent the tantalum surface ofsaid tantalum mesh and extending about the margins of said mesh, saidframework including a plurality ofelongated frame members and transverseframe members extending perpendicularly thereto at the ends thereof,said said frame members being fabricated of tantalum and said tantalumsurface of said mesh being bonded to said elongated frame members toprovide electrical connection therebetween resistant to corrosive actionby a bath in which the assembly may be disposed. said frame membersextending generally parallel to the plane of said mesh; and

a relatively rigid current distribution subassembly comprising at leastone elongated bus member extending in generally parallel relationship tosaid elongated frame members and to the plane of said mesh, saiddistribution subassembly further comprising at least one transverse busmember extending generally perpendicular to said elongated bus memberand disposed intermediate the ends of said elongated frame members andextending therebetween, said transverse bus member being bonded on onesurface thereof to said elongated bus member and on the other surfacethereof to the surface of said elongated frame members spaced from saidmesh to provide electrical connection therebetween resistant tocorrosive action by a bath in which the assembly may be disposed, saidbus members of said subassembly being free from electrical contact withsaid framework and said mesh except through the conductive pathsprovided by said bonds between the transverse bus member and theelongated frame members intermediate the length of said elongated framemembers for distribution of electrical current to said framework and tosaid tantalum mesh from points spaced intermediate the length of saidconductive framework.

2. The assembly of claim 1 further including insulating means disposedbetween said elongated bus members and said framework.

3. The assembly of claim 1 wherein said mesh is comprised of a pluralityof strips and wherein said framework has at least three elongated framemembers with two of said mesh strips being bonded to one of saidelongated frame members.

4. The assembly of claim 1 wherein said elongated and transverse busmembers are fabricated of tantalum.

5. The assembly of claim 1 wherein a plurality of elongated bus membersare provided and are bonded to a plurality of transverse bus membersdisposed intermediate the ends of said elongated frame members.

6. The assembly of claim 1 wherein said distribution subassemblyincludes at least two spaced elongated bus members and an additionaltransverse bus member electrically connecting said elongated bus membersat a point spaced along the length thereof and outwardly of saidconductive framework.

7. The assembly of claim 1 further including a support frame ofsynthetic plastic material supporting said conductive framework.

8. The assembly of claim 1 wherein said bus members are fabricated fromtantalum and wherein the surfaces of said bus members and frame membersexposed to the bath have a chemical compound formed thereon inert to andnon-conductive in the bath.

9. The assembly of claim 1 wherein said mesh is comprised of a pluralityof strips and said framework has at least three elongated frame membersand two transverse frame members disposed adjacent the ends thereof,with two of said mesh strips being bonded to one of said elongated framemembers, and wherein a plurality of elongated and transverse bus membersfabricated of tantalum are provided, at least some of said transversebus members being disposed intermediate the ends of said elongated busmembers.

1. A PLATINUM-CLAD TANTALUM ANODE ASSEMBLY COMPRISING: A RELATIVELYFLEXIBLE TANTALUM MESH HAVING PLATINUM CLADDING ON ONLY ONE SURFACETHEREOF AND A TANTALUM SURFACE; A RELATIVELY RIGID FRAMEWORRK DISPOSEDADJACENT THE TANTALUM SURFACE OF SAID TANTALUM MEASH AND EXTENDING ABOUTTHE MARGINS OF SAID MESH, SAID FRAMEWORK INCLUDING A PLURALITY OFELONGATED FRAME MEMBERS AND TRANSVERSE FRAME MEMBERS EXTENDINGPERPENDICULALY THERETO AT THE ENDS THEREOF, SAID SAID FRAME MEMBERSBEING FABRICATED OF TANTALUM AND SAID TANTALUM SURFACE OF SAID MESHBEING BONDED TO SAID ELONGATED FRAME MEMBERS TO PROVIDE ELECTRICALCONNECTION THEREBETWEEN RESISTANT TO CORROSIVE ACTION BY A BATH IN WHICHTHE ASSEMBLY MAY BE DISPOSED, SAID FRAME MEMBERS EXTENDING GENERALLYPARALLEL TO THE PLANE OF SAID MESH, AND A RELATIVELY RIGID CURRENTDISTRIBUTION SUBASSEMBLY COMPRISING AT LEAST ONE ELONGATED BUS MEMBEREXTENDING IN GENERALLY PARALLEL RELATIONSHIP TO SAID ELONGATED FRAMEMEMBERS AND TO THE PLANE OF SAID MESH, SAID DISTIBUTION SUBASSEMBLYFURTHER COMPRISING AT LEAST ONE TRANSVERSE BUS MEMBER EXTENDINGGENERALLY PERPENDICULAR TO SAID ELONGATED BUS MEMBER AND DISPOSEDINTERMEDIATE THE ENDS OF SAID ELONGATED FRAME MEMBERS AND EXTENDINGTHEREBETWEEN, SAID TRANSVERSE BUS MEMBER BEING BONDED ON ONE SURFACETHEREOF TO SID ELONGATED BUS MEMBER AND ON THE OTHER SURFACE THEREOF TOTHE SURFACE OF SAID ELONGATED FRAME MEMBERS SPACED FROM SAID MESH TOPROVIDE ELECTRICAL CONNECTION THEREBETWEEN RESISTANT TO CORROSIVE ACTIONBY A BATH IN WHICH THE ASSEMBLY MAY BE DISPOSED, SAID BUS MEMBERS OFSAID SUBASSEMBLY BEING FREE FROM ELECTRICAL CONTACT WITH SAID FRAMEWORKAND SAID MESH EXCEPT THROUGH THE CONDUCTIVE PATH PROVIDED BY SAID BONDSBETWEEN THE TRANSVERSE BUS MEMBER AND THE ELONGATED FRAME MEMBERSINTERMEDIATE THE LENGTH OF SAID ELONGATED FRAME MEMBERS FOR DISTRIBUTIONOF ELECTRCAL CURRENT TO SAID FRAMEWORK AND TO SAID TANTALUM MESH FROMPOINTS SPACED INTERMEDIATE THE LENGTH OF SAID CONDUCTIVE FRAMEWORK 2.The assembly of claim 1 further including insulating means disposedbetween said elongated bus members and said framework.
 3. The assemblyof claim 1 wherein said mesh is comprised of a plurality of strips andwherein said framework has at least three elongated frame members withtwo of said mesh strips being bonded to one of said elongated framemembers.
 4. The assembly of claim 1 wherein said elongated andtransverse bus members are fabricated of tantalum.
 5. The assembly ofclaim 1 wherein a plurality of elongated bus members are provided andare bonded to a plurality of transverse bus members disposedintermediate the ends of said elongated frame members.
 6. The assemblyof claim 1 wherein said distribution subassembly includes at least twospaced elongated bus members and an additional transverse bus memberelectrically connecting said elongated bus members at a point spacedalong the length thereof and outwardly of said conductive framework. 7.The assembly of claim 1 further including a support frame of syntheticplastic material supporting said conductive framework.
 8. The assemblyof claim 1 wherein said bus members are fabricated from tantalum andwherein the surfaces of said bus members and frame members exposed tothe bath have a chemical compound formed thereon inert to andnon-conductive in the bath.
 9. The assembly of claim 1 wherein said meshis comprised of a plurality of strips and said framework has at leastthree elongated frame members and two transverse frame members disposedadjacent the ends thereof, with two of said mesh strips being bonded toone of said elongated frame members, and wherein a plurality ofelongated and transverse bus members fabricated of tantalum areprovided, at least some of said transverse bus members being disposedintermediate the ends of said elongated bus members.